Motor, as a power producer, is widely applied in the field of automatic control technology. For example, motors are used as drivers for shafts in robots and robotic arms used in a variety of industries, such as TFT-LED display, automobile and the like. To ensure that a robot or a robotic arm can carry out predetermined actions, a drive circuit is needed to bring the motor which drives the robot or the robotic arm into operation, and a brake control circuit is needed to stop the motor from operating.
FIG. 1 illustrates a motor brake control circuit commonly used in the prior art, which comprises a brake control input module 100 and a brake control main module 200. A control signal input unit 110 in the brake control input module 100 is used to introduce an external control signal from the outside and output a brake control signal in case of an external control signal. In the brake control main module 200, a brake control output unit 230 is used to output a brake signal to a motor brake (not shown), and a power input unit 210 is used to import a power signal which, under the control of the brake control input module 100, is transmitted to the brake control output unit 230 after rectified by a rectifying circuit 220 (a half-wave rectifying circuit in FIG. 1) and then transmitted to the motor brake via the brake control output unit 230, so as to stop the motor.
In the control process of a motor, in the case of normal operation, the output end of the control signal input unit 110 is at a high level (i.e. no brake control signal) so that normally open contacts of a relay 120 are closed. Therefore, the power signal introduced from the power input unit 210 is output to the motor brake via the brake control output unit 230 after rectified by the rectifying circuit 220 as a maintaining voltage indicating no need of brake, and thus the motor brake is not activated and the motor is not locked. In the case that the power is off or an emergency stop button is pressed, the control signal input unit 110 connected to the outside generates a brake control signal of low level at its output end according to the received power-off signal or the emergency stop signal. Accordingly, the commonly open contact of the relay 120 is open, the power signal is cut off, and no voltage is output from the brake control output unit 230. In this way, the motor brake works to lock the motor.
As shown in FIG. 1, the rectifying unit 220 is generally formed by a plurality of discrete components. When aging, damage or failure happens to one of these components in the rectifying unit 220, the brake control output unit 230 cannot output the maintaining voltage. As a result, the motor brake is mistakenly activated to lock the motor, and thereby the robot or the robotic arm cannot operate properly. When such malfunction occurs, one currently-adopted solution is replacing the whole brake control board, which is costly. Another solution is disassembling and replacing the rectifying unit 220 or repairing the rectifying unit 220, which is cumbersome and time-consuming, as the component(s) causing this malfunction needs to be found out, thus extending downtime and increasing production cost.
Meanwhile, in FIG. 1, in the case of unstable peak voltage of the power signal, frequent use of the relay, exception/failure of components, and end of service life of selected components, the following situations may occur: in need of braking, the commonly open contacts of the relay 120 cannot be open promptly or all along, which disables the maintaining voltage at the brake control output unit 230 from disconnecting, and causes malfunction of the motor brake, and thus the motor cannot be locked. This may bring harm to personal safety of an equipment user and may cause loss to the production.
In order to avoid the above situations, currently, it becomes an urgent task to design a motor brake control circuit which is of high brake reliability and convenient for maintenance.